Why Are Your Tomato Leaves Turning Black?

Gardening can be a rewarding and enjoyable hobby, but it also comes with its fair share of challenges. One common problem that tomato gardeners face is the phenomenon of tomato leaves turning black or brown. This can be a cause for concern, as it may indicate underlying issues with the plants’ health. In this article, we will explore some of the main reasons why tomato leaves turn black and provide tips on how to improve the overall well-being of your tomato plants.

Understanding the Causes

Tomato leaves can turn black due to various factors, including temperature stress, diseases, or herbicide injury. Let’s delve into each of these causes in more detail and discuss preventive measures.

Frost

Frost damage is the most common reason why tomato leaves turn dark green or black. Tomatoes are warm-weather crops and are not tolerant of frost. Therefore, when exposed to freezing temperatures, they can suffer significant damage. The appearance of frost damage can vary depending on several factors, such as weather conditions, the size and age of the tomato plant, leaf health, tomato variety, and topography. It is crucial to wait until the plant has thawed before assessing the extent of the damage.

To prevent frost damage, it is advisable to plant your tomatoes after the last spring frost. Additionally, you can use protective measures such as row covers, water walls, cloches, or hoop houses to insulate the plants and shield them from cold temperatures.

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Early Blight

Early blight is a plant disease that affects tomatoes and other nightshades. It is characterized by dark yellow leaves, brown or black leaf edges, dark lesion spots on stems, and leathery, dark spots on the fruit. This disease thrives in warm and wet weather conditions, particularly in humid regions. Early blight is caused by pathogens that reside in the soil and enter the plant through soil splashing or contact with infected surfaces.

To prevent early blight, it is crucial to choose disease-resistant tomato varieties and acquire healthy starts. Limiting soil splash by using mulch or landscape fabric and maintaining adequate spacing between plants can also help reduce the spread of the disease. Avoid working among tomato plants when their leaves are wet, as moisture facilitates the easy transmission of the pathogens. Proper sanitation, such as removing infected plant debris and practicing crop rotation, is vital in preventing the overwintering of the disease.

Late Blight

Late blight is a destructive disease that affects tomatoes and potatoes. It was responsible for the infamous Irish potato famine. Late blight is caused by a wind-blown pathogen that spreads rapidly in cool and wet weather conditions. The disease begins as dark brown blotches on the leaves, which eventually spread to the entire plant. Late blight can cause tomato leaves to turn brown or black, ultimately leading to plant death.

Preventing late blight involves following similar cultural controls as for early blight. It is essential to avoid working in wet conditions and purchase disease-free certified potatoes and healthy tomato plants. Additionally, refraining from planting volunteer plants can minimize the risk of carrying infections from the previous year.

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Herbicide Injury

Gardens located near roadways, utilities, or conventional agricultural fields are at risk of herbicide injury. Herbicides, which are chemicals designed to kill plants, can drift on the wind and come into contact with susceptible garden plants. Herbicide injury in tomatoes often manifests as warped, twisted, or stunted leaves and stems, curled leaf appearance, and changes in leaf color.

Preventing herbicide injury is challenging, but gardeners can take proactive steps such as using row covers to limit the contact between herbicides and plants. Engaging in conversations with individuals responsible for spraying herbicides and posting “do not spray” signs around your property can also be effective deterrents.

Conclusion

Tomato leaves turning black can be a cause for concern for any gardener. By understanding the various causes of this issue and implementing appropriate preventive measures, you can ensure the well-being and productivity of your tomato plants. Remember to choose disease-resistant varieties, practice proper sanitation, and protect your plants from extreme temperatures and external factors that may harm them. Happy gardening!

Ames Farm Center